Homo floresiensis: More on Microcephaly

According to New Scientist a new study will be published in Science indicating that Homo floresiensis was a microcephalic member of a dwarved population (splitting the difference I guess). The study modelled dwarfism in a range of mammals:

“As they dwarf, species’ brain sizes decline far more slowly than body size,” says Ann MacLarnon from Roehampton University, UK, who modelled dwarfing in a range of mammals from dogs to elephants with a team from the Field Museum, Chicago, US. “Brain size is key to a mammal species’ identity,” she says. There is, for example, hardly any difference in brain size between the smallest modern humans, the 1.4-metre Bambuti people of Congo’s Ituri Forest, and the tallest, the 2-metre Masai of east Africa.
The team calculated that a dwarfed H. erectus with a 400cc brain would weigh just 2 kilograms. “That’s one-tenth of what the Flores people must have weighed,” she explains. The only way to explain the discrepancy, the team believes, is microcephaly.


Morwood disputes this:

“Although we only have one cranium,” says Morwood, “the other bones we found show that LB1 was a normal member of an endemically dwarfed hominid population.” The distinctive traits of reduced body mass, reduced brain size and short thick legs mirror those found in other island endemic populations of large mammals, Morwood says. He calls the microcephaly explanation “bizarre”. It ignores other evidence from Liang Bua and the literature on island endemic evolution, he says.

As soon as I track the article down I will have more to say on the subject…
MSNBC also has an article on it:

In a response to their paper, researchers led by Dean Falk of Florida State University called Martin’s assertions “unsubstantiated.” Martin’s comparison of LB1 with the skulls of microcephalics lacks crucial details, Falk stated.
Falk also challenged Martin’s comment that such a small brain size would indicate an extremely tiny creature based on the calculations for dwarf versions of other animals. It would be surprising if the dwarf version of an early human scaled down in the same way as an elephant, for example, Falk responded.
Falk and his co-authors argued that the size of LB1’s brain is consistent with that of adult microencephalics.

Weird, first Falk is qouted as dismissing the microcephaly argument then supporting it, I think the reporter was confused…
hobbit-1_big.jpg
National Geographic has more:

The disease has dozens of different forms, Martin says. But Falk and colleagues only compare the Flores fossil to one poorly matched microcephalic skull of a modern human.
Martin’s team, by contrast, identified other microcephalic skulls that more closely resemble the Flores fossil skulls, he says.
Falk acknowledges that her team only examined one skull. But she adds that the evidence that Martin’s team’s skulls are better matched is poorly illustrated in Martin’s paper.
Regardless, Falk adds, her team is finishing up an in-depth analysis on microcephaly.
“We’re confident that [the hobbit skull] is not a microcephalic,” she said.
Also, Falk and her colleagues noted in their original paper that normal dwarfing of H. erectus could not explain the Flores fossils.
Rather, they suggested the hobbits resulted from dwarfing of apes or australopithecines, earlier human ancestors.

*snip*

Potts says Martin and colleagues are primarily reacting to the original interpretation of the hobbit find, published in 2004 in the journal Nature.
That study said that the Flores fossils represent island dwarfing in H. erectus and not dwarfing of an ape or australopithecine.
“So what would island dwarfing in an ape look like?” Potts asked. “We don’t know–that’s one of the big gaps of this whole thing.”
In addition, Potts says, Martin and colleagues’ suggestion that the Flores skull represents a microcephalic modern human is unsupported by recent studies on leg and shoulder fossils from Flores that suggest similarities to earlier human ancestors.
“We’re dealing with something unprecedented in modern humans,” Potts said.
“[The hobbit is] either a representative of a unique and unreported range of variation in a modern human, or it’s a new species that seems to be derived from an earlier ancestor.
“That second idea is more in line with the original interpretation and probably the safest at this stage,” he continued.
“But it’s a wonderful mystery.”

4 Responses

  1. Isn’t microcephaly commonly accompanied by mental retardation? What chances a mentally retarded population have at surviving?

  2. As I understand it, there are other pathologies in cases of microcephaly not found in the H. floresiensis skull. Then you have the fact older remains have been found going back thousands of years. No skulls, yet, but other parts of the skeleton. If all of these were microcephalics, where are the normals? Where are the people who gave birth to them? Or do we have the first case of a race of microcephalics?
    Methinks that by concentrating on one subject and ignoring others some people are formulating bad hypotheses.

  3. The argument from cranial morphology that Homo floriensis (HF) descends from Homo erectus (HE) seems strong, while arguments against seem weak. It is easy to see also, that the HF thesis is likely to be easily further corroborated.
    Has anybody thought of arguing that HF was tolerated by Homo sapiens (HS), while most other HE descendants were not, because he lived in caves on a remote island AND was very small?!? Such tolerance would also explain how HF came to have modern tools: Obviously via trade with coastal HS, at least originally.
    It is after all, only the idea of the design of modern tools which is necessarily modern. Once HE sees the modern design idea, he may be quite capable of adopting it. HE may even have been taught how to make modern tools by HS.
    As a 4th-generational Tasmanian, I know how islanders (HE, HF, HS) are of necessity more co-operative than mainlanders, and that island coastal peoples interests often end at the uplands or mountains. Humans have always been dreamers interested in fairy tales also.
    So it is easy for me to imagine a traditional mutual co-existence developing on Flores between coastal HS and mountain HF, continuing right up to European colonisation, as oral history suggests indeed happened.

  4. New to paleo-archaeological debates, I see how the field is unnecessarily diminished by the historical division between “out of Africa” and “regionalist” camps, in the Homo floresiensis discussion for example. Human mitochondrial DNA (mtDNA)/Y-chromosome phylogeography shows very strongly that homo sapiens came “out of Africa”.
    But such explanation is generally too totalistic. Both sides tend to illogically totalise, fail to mention or see that, while homo sapiens and the hominid genus almost certainly came “out of Africa”, Homo Erectus probably came out of Asia (Kohn 2006). Some homo erectus ancestors and other hominids may also have come “out of Asia”.
    This difference between homo erectus, homo sapiens centres of endemism is very telling, has implications. As I explain in (paper 5 page 6 of) my ebook at http://www.nodrift.com/vol_5/5.1.pdf :
    “SEXUAL SELECTION THUS MOST IMPORTANT FOR HOMO SAPIENS
    . . . evolutionary considerations AND homo sapiens evolving in AA Africa, coming “Out of [AA] Africa”, not “Out of [IR] Asia”, page 5, imply a corollary:
    Conventions are very much a product of sexual selection. Sexual selection has thus evidently been more important than natural selection in evolution of homo sapiens, in contrast to evolution of homo erectus, where natural selection may have been more important than sexual selection.”

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